Ground trainer for aircraft flight personnel



July 25, 1950 R. o; RIPPERE GROUND lrRAINER RoR AIRCRAFT FLIGHT PERSONNEL 4 Sheets-Sheet 1 EIIed June 14, 194e m. No?.

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ATTORNE V July 25, 1950 R. '0. RIPPERE GROUND TRAINER FoR AIRCRAFT FLIGHT PERSONNEL 4 Sheets-Sheet 2 Filed June 14, 1946 QON) /N VEN ron R. O. R/PPERE A TTORNE V July 25, 1950 R. o. RIPPERE GRoUND rI'RAINER FoR AIRCRAFT FLIGHT PERSONNEL 4 Sheets-Sheet 15 /NVEN'OR B 0. R/PPERE 6? M' QOL UM 4MM. NVM.

Filed June 14, 1946 ATTORNEY R. o. RIPPERE GROUND TRAINER RoRY AIRCRAFT FLIGHT PERSONNEL July 25, 1950 4 Sheets-Sheet 4 Filed June 14, 1946 ovv i w Qi n? 21mm ...MQW

/N VE N TOR R. V o. R/PPERE @56. M

A T TOR/VE V lUNITED STATES ATENT lOFFICE GROUND TRAINER FOR AIRCRAFT FLIGHT PERSONNEL Robert 0. Rippere, Massapequa, N. Y., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application June 14, 1946, Serial No. 676,603

Claims.

This invention relates to a ground trainer for aircraft flight personnel and more particularly to circuits and apparatus which simulate the .hydraulic system of an airplane and the functioning of apparatus of an airplane which is operated by hydraulic pressure applied from the hydraulic system.

In an airplane of the type which the trainer of the present invention is designed to simulate a mixed open-center and constant pressure type of hydraulic system is provided. The open-center portion of the system is used to raise and lower the landing gear, to open and close the bomb bay doors, and to extend and retract the wing `flaps. The constant pressure portion of the system is used for the brakes, for the einergency operation of the bomb doors, for the automatic pilot and to operate the windshield wipers.

An uploader valve directs hydraulic fluid from the open-center system to the constant pressure system when the accumulated pressure for the latter drops below 850 pounds per square inch.

Normally uid is pumped from a reservoir through a supply line forming a part of the opencenter system through check Valves. to the two accumulators of the constant pressure portion of the system which supply pressure for operating the right and left brakes respectively, and to Ian unloader valve. When the pressure in the accumulators reaches 1,050 pounds per square inch, the unloader valve functions to extend the supply line in a loop through the bomb bay door selector valve, through the wing iiap selector valve and through the landing gear selector valve back to the reservoir thereby completing the open-center portion of the system. The pressure in the open-center system then falls to about 50 pounds per square inch until one of the selector valves is operated whereupon it will build up to a value required to operate the mechanism controlled by such Valve. When the pressure in the accumulators falls to 850 pounds per square inch the unloader valve functions to dis-- connect the supply line from the selector valves whereupon the pressure in the accumulators will again build up.

The selector valves are so constructed that when one of them, for example, the landing gear selector valve, is operated to one of its control positions, as to retract the landing gear, the engine pump side of the open-center system becomes disconnected from the fluid reservoir and connected to the ports of the landing gear operating cylinders required to move the pistons to raise the landing gear. For this purpose the pressure will build up to about 800 pounds per square inch. After the landing gear has been moved to its full up position the pressure in the valve will continue to build up to about 1,040 pounds per square inch when it is eifective to .operatev a hydraulic detent in the valve to release the valve stern which then returns under spring tension to its neutral position, and the pressure supply line from the pump becomes reconnected to the fluid reservoir and the pressure in the open-center system then again drops to 50 pounds per square inch.

An auxiliary electrically driven pump may be used either for charging the accumulators only, 'or to operate the entire hydraulicsystem. When the emergency cross-over valve is closed iiuid Bows from the auxiliary pump directly to the accumulators and under this condition the pump is governed by a pressure switch which maintains the accumulator pressures between 975 and 1,140 pounds per square inch. Opening this valve allows fluid to flow to the unloader valve either supplementing or replacing the flow from the pump driven by the No. 3 engine.

An emergency hand pump may be used to furnish fluid pressure to lower the wing Iiaps or to operate the entire hydraulic system. A relief valve is also provided to prevent the pres- `sure from exceeding 1,250 pounds per square inch.

It is any object of the invention to simulate in a trainer the functioning of the hydraulic system of an airplane of the type just described.

It is a further obj ect of the invention to simulate in a trainer by electrical means the functioning of the hydraulic system of an airplane during the loperation of the landing gear, wing flaps and brakes under regular, auxiliary and emergency conditions.

These and other objects pertinent thereto are attained by the structure set forth in the appended claims and discussed in the following detailed. description when read in connection with the accompanying drawings in which:

Fig. l discloses in the left portion thereof indicators on the pilots instrument panel, landing gear control lever, wing flaps control lever and parking brake lever; in the box in the upper portion thereof signal lamps and control keys at the instructors desk and in the remainder of the gure some of the relays and circuits which simulate the functioning of the hydraulic system of an air-plane in response to controls operated by the pilot and by an instructor;

Fig. 2 discloses in the left portion thereof switches and potentiometers operable in response to the operation of the brake pedals situated in front of the pilots and copilots seat, the hydraulic hand pump located at. the right of the copilots seat, the master ignition switch located above the 'pilots pedestal, the battery switches on the copilots power panel at the right of his seat and the forward and aft emergency ap lowering valves located at the right of the copilots seat; in the upper right portion thereof relays controllable by the ignition and battery switches and representations of the indicated air speed motor unit, altimeter motor unit and the R. P. M. motor unit corresponding to one of the simulated engines;

Fig. 3 discloses in the upper portion thereof other controls, signal lamps and indicators at the instructors desk, which indicators are operated in -parallel with similar indicators on the pilots instrument panel and in the remainder of the figure the remaining relays and circuits which simulate the functioning of the hydraulic system of an airplane in response to controls operated by the pilot and by the instructor and in response to the operation of the motor units of Fig. 4;

Fig. 4 discloses the motor unit which simulates the production of pressure in the constant pressure portion of the hydraulic system and the motor units which simulate the Wing flaps and landing gear hydraulic mechanisms; and

Fig. 5 is a chart showing how Figs. 1 to 4, inclusive, should be arranged to completely disclose the invention.

The controls shown in the left portions of Figs. 1 and 2 are similar to the controls which would be found in an actual airplane but have been modied by the addition of cam-operated contacts and potentiometers in order that their operations which normally would control valves of the hydraulic system, may be simulated electrically.

Each of the motor units of Fig. 4 comprises a motor of the alternating current shaded pole type having a main eld winding energized from a source of alternating current and two shaded pole windings one of which when short-circuited will cause the rotor of the motor to be turned in one direction of rotation and the other of which when short-circuited will cause the rotor of the motor to be turned in the opposite direction of rotation. The rotor turns a shaft having switch operating cams thereon and through gearing may operate the sliders of one or more potentiometers.

The indicated air speed, altimeter and R. P. M. motor units of Fig. 2 are of the type disclosed in the application of Albert, Davis, Gumley and Holden, Serial No. 502,484, led September 15, 1943. This application has since matured into lbatent No. 2,428,767, dated October 14, 1947.

These motor units would be controlled to position y their shafts into positions representative of the indicated air speed, altitude and engine speed in response to the operation of the flight and engine controls of the trainer in the general manner disclosed in the application of R. C. Davis, E. J. Fogarty and R. O. Rippere, Serial No. 542,986, filed June 30, 1944.

To prepare the trainer for simulating the operation of an airplane the master ignition switch No, sometimes called the crash bar, must be in the closed position thereby establishing an obvious circuit for the MB relay 261, and the circuit breaker switches 20'2 and 283 should be closed thereby causing the operation of the RB and LB relays 204 and M5 representative of the application of power from the storage battery to the right and left portions of the airplane. In an actual airplane the master ignition switch when operated enables the ignition circuits of the engines and connects the battery bus bar, from which battery power is supplied to the airplane, to the storage battery. If a crash seems imminent this switch may be operated to the off position in which the engine magnetos all become grounded thereby stopping the engines and the battery circuit is opened leaving no electric current on the airplane.

In the trainer when the starting of the No. 3 engine is simulated the shaft Zil of the R. P. M. motor unit of Fig. 2 assumes a position representative of the speed of rotation of such engine and the cam 231 moves from its normal position to permit the closure of the contacts of the Li limit switch thereby closing the circuit of the ON relay 298. This relay, upon operating, in addition to establishing other circuits representative of the fact that the engine is started, closes a circuit extending from ground over contacts of such relay and over conductor 209 through the winding of the ENG relay 40B of Fig. 1 to battery. Relay il now operates representative of the operation of the hydraulic pump driven by the No. 3 engine of the actual airplane.

Relay Ii, upon operating, establishes the circuit of the HP relay ll over a circuit extending from ground, over the inner upper contacts of relay H3G, over the lower contacts of the Main Hydraulic key H32 at the instructors desk and through the winding of relay lill to battery. Relay Hl! operates to represent the creation of hydraulic pressure by the pump driven by the No. 3 engine. Relay 189 also establishes a circuit for the charge accumulator (CA) relay Sill! since at this time there might be no simulated pressure in the accumulatore of the hydraulic system. This circuit may be traced from ground over the upper contacts of relay lill), over conductor w3', over the contacts of the BP-LZ limit switch of the brake pressure motor unit of Fig. 4 and over conductor 138i! through the winding of the C'A relay 363 to battery.

Relay 330, which simulates the function of the unloader valve of an actual airplane, upon operating establishes over its upper contacts and conductor 601, a short circuit of the right shaded pole winding 402 of motor 483, and with the main stator winding 464 of the motor energized from the alternating current source 4&5, the motor will turn the shaft 4&6 at a slow speed in a counterclockwise direction whereby through the gears lill and 498 the slider1 of potentiometer BPH! is moved toward the No. 3 terminal of the potentiometer winding. The winding of this potentiometer is energized over a direct current path from battery through resistor 499, through the potentiometer winding and through resistor 410. Thus as the slider moves from the No. l terminal towards the No. 3 terminal of the potentiometer winding an increasing potential is derived at the potentiometer slider and applied over conductor 4i l, over the lower back contact of the accumulator empty (AE) relay Sill, through resistor 302 to conductor 303 and thence in parallel to one control conductor of the inboard and outboard brake pressure indicators 384 and 305 at the instructors desk and inparallelto oneconductor of the coriresponding indicators 104 and 105 on thepilots instrument panel. These indicators are of the direct current selsyn type. Since the other two control conductors from these indicators are also connected in parallel over conductors 306 and 30'1 to taps on the potential divider 308, Apotentials of dii-ferent Value are also applied to such other control conductors and due to the changing potential applied from the slider of potentiometer BPH! the needles of the indicators will be moved to represent an increasing fluid pressure in the constant pressure portio'noi the simulated hydraulic system. The potential divider 308 comprises the resistors 309, 310 and 311 connected in series between battery and ground.

With the CArelay 300 operated, potential from the slider of potentiometer BP is also applied over the lower front contact of relay` 300, through resistor 312 to conductor 313 and thence in parallel to one control conductor of the hydraulic pressure indicators 314 and 114 at the instructors desk and on the pilots instrument panel, respectively. The two other control conductors of these indicators are connected in parallel over conductors 315 and 311i to taps on the potential divider 31'1 whereby potentials of different values are applied to such control conductors. The potential divider 311 comprises the resistors 318, 319 and 320 connected in series between battery and ground. Thus as the slider of potentiometer BP10 moves, representative of an increase in fluid' pressure, the needles of the indicators 314 and 114 will move to show the same increase in pressure as the indicators 304, 305, 104 and 105.

Violent movements of the needles of the hydraulic pressure indicators 314 and 114 are prevented by using the charging time of condenser 32| which charges over a circuit traced from the slider of potentiometer BP10 through resistor 312.

When the motor 403 has turned the slider of potentiometer BP10 to a position representative of a pressure of 1,125 pounds per square inch, the limit switch BP-L2 will be operated to the open Contact position thereby opening the previously traced circuit of the CA relay 300 which will thereupon release to open the short circuit of the shaded pole winding 402 of motor 403 whereupon the motor will come to rest. The release of relay 300 also removes the potential applied from the slider of potentiometer BP10 to the hydraulic indicators 314 and 114 whereupon such indicators will show a decrease in pressure to 50 pounds per square inch as determined by potential applied thereto through resistor 312, over the back contact of relay 300 from a tap on the potential divider comprising resistors 322 'and 106 connected in a series circuit from battery through resistor |06, over the upper contacts of the operatedv I-IP relay 101, over conductor 101, over the normally closed front contact of the slow-to-release relay 323 and through resistor 322 to ground. This reduction in pressure indication is representative of the pressure in the opencenter portion of the hydraulic system of an airplane after the accumulators have become charged and the unloader valve has operated. The brake pressure indicators continue to read the accumulator pressures of 1,125 pounds per square inch.

The instructor can simulate the failure of the open-center portion of the hydraulic system by operating the Main Hydraulic key 102 to its open position thereby opening the circuit` of the lHP relay 101. EThe Apotential divider circuit 'coil2 trolled by relay 101` will now be opened and the hydraulic pressure indicators 314 and |14 which indicate the pressure in the open-center portion ofthe system willnow show a decrease in pressure to fzero, .With relay 101 thus deenergized to represent the failure of pressure in the opencenter system the wing flaps and landing gear motor units which simulate the hydraulic operation of the wing flaps and landing gear cannot be operated from the simulated open-center system as will be hereinafter described. The operation of switch`102 does not prevent the simulation of the emergency lowering of the wing flaps by direct hand pump operation and does not disable the brake pressure system.

The pilot may supplement the pressure derived from the engine driven pump by starting an auxiliary electric motor driven pump through the operation of the Hydro Booster circuit breaker switch 108 located on the pilots pedestal. In the trainer the operation of the electric pump is simulatedby the operation of the electric pump (EP) relay 109,'the circuit of 'which is established by the operation of the electric pump circuit breaker (EPCB) relay I 10 when the circuit breaker switch 108 is closed, if the master battery (MB) relay 201 and either the left or right battery (LB or RB) relays 204 and 205 or both have been operated as previously described. With relays 201, 204 and 205 and 110 all operated the circuit of relay 109 may be traced from ground over contacts of either or both relays 204 and 205, over the backcontact of battery cut-oil" (BCO) relay 210, over the contacts of relay 201, conductor 21 1, over the upper front contacts of relay 110 and through the winding of relay to battery.

If the engine is running and the ENGl relay 100 is operated, the operation of the EP relay |09 establishes a supplementary ground to conductor 103, over its upper contacts and over the lower normal contacts of the Electric Pump disabling key 11i at the instructors desk whereby the circuit of the CA relay 300 is maintained after the simulated disabling of the engine driven pump is represented by the disabling of the engine. If the engine driven pump of the airplane fails and the electric pump is started, a cross-over valve may be operated to permit the electric pump to produce pressure for normal operation of landing gear, wing flaps, and bomb doors. In the trainer the function of the cross-over valve is simulated by the operation of the Emergency Shut-01T Valve key 112 at the instructors desk. With the engine assumed to be disabled, as simulated by the release of ENG relay 100, the previously traced circuit for the HP relay 101 is opened but with the EP relay 109 operated and key 112 also operated, relay |01 is maintained operated in a circuit from ground over the upper contacts of key 111, contacts of key 112, the inner upper contacts of relay 109, the lower contacts of key 102 and through the winding of relay 101 to battery. Under this condition with relays 109 and 10| both operated, the maintenance of pressure in both the open-center and constant pressure portions of the hydraulic system is maintained. The pilot will request the instructor to operate the key 112 when he desires such key to be operated as he would instruct' a member of the airplane crew to operate the crossover valve.

Under these conditions if the instructor operates the Main Hydraulic Line key 102 to its open oridi'sable position, u the disabling of the openenter portion ofthe hydraulic system is simulated and if the Electric Pump disable key Hl is operated to its open or disable position the circuits for both the HP and CA relays 10| and 390 are opened and the ydisabling of the entire .hydraulic system is thus simulated. The hydraulic pressure indicators will then operate to show a reduction of pressure in the open-center portion of the system to zero but the brake pressure indicators will still indicate the accumulator pressures previously established by the operation of the brake pressure motor unit. The simulation of the disabling of the electric pump may be accomplished by the instructor by the operation of the Hydro Booster circuit breaker switch H3 whereby direct battery is connected between the circuit breaker switch |08 at the pilots pedestal and the winding of relay |51! to cause the `circuit breaker switch to open and to cause relay i I to release and in turn to release the EP relay |09. Relay HD upon releasing opens the circuit of Hydrov Booster Emergency lamp H at the instructors desk, which lamp lighted when the pilot operated switch |08, to inform the instructor that the pilot had resorted to the use of the electric pump. Relay H0 also establishes the circuit of the Hydro Booster lamp H6 which lights :and remains lighted until the pilot restores the circuit breaker switch |18.

In the event both the engine driven pump and the electric motor driven pump frail the copilot may supply hydraulic pressure in an actual airplane by the operation of the emergency hand pump located at the right of his seat. In the trainer the hand pump is provided with a switch 2|2 which is operated by the forward and backward movement of the pump handle 2|3, as disclosed in Fig. 2, to alternately close the circuit extending over conductors 2|# and 2|5 through the -windings of the pump handle up (PU) and pump handle down (PD) relays H1 and H8, respectively. These relays operate in alternation and being slow to release both will be operated during the interval required for one of them to release. During the time both are operated a circuit is established over their lower contacts through the Hand Pump lamp H9 at the instructors desk to inform the instructor that the hand pump is being used.

At this time the Forward Emergency Flap Lowering Valve 2|6 is open and the Aft Einergency Flap Lowering Valve 2H is closed and consequently the circuits controlled by the switches associated therewith extending to the windings of the forward valve (FV) relay |21) and to the winding of the aft valve (AV) relay 12| will be opened. Thus during each interval that the relays and H3 are both Ioperated a :circuit will be established for the HP relay |0| which may be traced from ground over the upper front contacts of relays H8 and H1, over the upper back contact of the FV relay |20, over vthe lower contacts oi key |02 and through the winding of the HP relay |0| to battery. With relay |01 thus operated it will be possible, as later described, to simulate the operation of the landing gear .or of the wing flaps. A circuit is lalso yestablished from gro-und over the inner upper contacts of relays HS `and H1 and over the inner upper bac-k contact of the FV relay |26 to conductor |03 Aand thence as traced through the winding of the CA relay 30|] to battery whereby such latter relay may be operated to control the brake pressure motor unit in simu-lation of the increase of pressure in the accumulators which would result .from

the operation of the hand pump. Since the circuits of the HP relay ||l| and of the CA rel-ay 3BG are closed only intermittently -when both relays lla and H1 are operated, relays |0| and -300 will follow the hand pump operation and the brake pressure and hydraulic pressure indicators will consequently show iiuctuating indications.

Should the instructorl now operate the Main Hydraulic Line key ||l2 to its disable position the circuit of relay |0| will be opened thus simulating the disabling of the open-center portion of the system and the operation of the wing iiaps yor landing gear may not then be simulated.

Landing gear operation In the actual airpl-ane to prevent the retraction of the landing gear while the airplane is on the ground, an electromechanical lock is provided which prevents the pilot from moving the landing gear selector control to the up position until the airplane has left the ground. In the trainer the solenoid |22 is provided to prevent the valvestem |23 of the hydraulic valve |24 operable by the Landing Gear Selector lever |25 from moving to its up position. This solenoid can only be energized after an airborne condition of flight has been simulated by the release of the G4 relay 2|8, associated with the altimeter m-otor unit of the trainer. This relay released when the Li and L3 switches of such unit moved to represent an airborne condition. Thereafter if the Landing Gear Safety (LS) relay |26 has been Ioperated by the previous closure of the circuit breaker switch |21, the pilot may unlock the landing gear control lever by depressing the button |28 located in the top of the lever thereby establishing a circuit for locking solenoid |22 which may be traced from battery through the winding of solenoid `|22, over the contacts of switch |28, over the contacts of relay |26, conductor |29 and t0 ground at the back contact of relay 2 |18. The altimeter motor unit functions in the manner described in the application, 4Serial No. 542,986, hereinbefore referred to.

With the lock now removed by the operation of solenoid |22 the pilot may now move lever |25 to the right or up position. With the valve stem operated to its up position the contacts |-3| are closed thereby establishing a circuit from ground thereover, over conductor l|32 and through the winding of the leading gear up (GU) relay 324. This relay upon operating establishes over its upper contacts and conductor 325, a circuit for the Landing Gear Selector Up lamp |33 at the instructors desk to inform the instructor that the pilot has operated the landing gear selector to its up position. At its inner upper contacts relay 324 establishes a locking circuit for the HPI relay |34, which operated following the operation of the HP relay mi over an obvious circuit. The locking circuit for relay |34 may be traced from battery through the winding and upper contacts of relay |34, 4over the upper contacts of key |82 at the instructors desk, over conductor |35 and to ground over Ithe inner upper contacts of relay 324. 'This locking circuit prevents `the release of relay |34 during the time that the landing gear selector is in the up position except through the operation of the disable key |132 by the instructor. Relay 324 also establishes a circuit from ground over its lower middle contact., over conductor 326, over the upper back contact of the LI relay 4|2, over conduc-tor M3 and through the winding of the DGU relay 321 to battery.

Relay 321 upon operating establishes a circuit from ground over its upper contacts and conductor 328 and through the winding of solenoid |36 to battery, which operates to position the locking detent |30 of the hydraulic valve, |24 to lock the valve stem |23 in its operated up posi` tion. Relay 321 also establishes a circuit from battery through resistor |31, over the lower contacts of the EPI relay |34 over conductor |38, over the back` contact of the KGU relay 329, over the inner upper contacts of relay 321, through resistor 330, over the front contacts of the RV2 relay 323 and through resistor 322 to ground. Potential derived from this potential divider is applied over the lower back contact of the CA relay 300 and through resistor 3|2 tothe hydraulic pressure' indicators H4 and 3M whereupon such indicators are operated to show a pressure of 800 pounds per square inch representative of the pressure which would be applied from the open-center system of an airplane to the landing gear operating cylinders.

, Relay 321 also establishes a circuit from ground over the inner lower iront contact oi the HP relay over the upper back contacts of the FD relay |39 and the FU relay |40, over conductor isi, over the lower contacts of relay 321, over conductor l364 and through the right shaded pole winding 3|@ of the motor vliti or the landing gear motor unit of Fig. l to ground. Since the stator winding M3 of this motor is energized from the alternating current source 405, the motor now turns the shaft 4|1 and through the gears H8 and 4|3 turns the slider of potentiometer LG? from the No. 3 terminal toward the No. 1 terminal of the potentiometer winding representative of the retraction of the landing gear. When the cam 442 closes the contact of limit switch LG-L| as the slider approaches the No, l.

terminal of the potentiometer winding, an obvious circuit is established for the LI relay M2. Relay M2 upon operating also connects ground over its lower contacts to control conductors 420 and 42| extending through cable 422 to the Landing Wheel Fla-ps Indicators 342 and |42 on the instructors and pilots instrument panels to cause such indicators to indicate the movement of the landing gear to the up position. At its upper contact relay 4|2 opens the previously traced circuit for the DGU relay 321 and closes the circuit of the KGU relay 329. Relay 321 upon releasing opens the short circuit of the right i shaded pole winding 4&4 of the motor `415 there-- by stopping the motor.

Relay 321 is slow to release and therefore does not open the potential divider circuit previously traced through resistors |31, 330 and 322 until after relay 323 has operated to establish the potential divider circuit extending as previously traced from battery through resistor l31 to conductor 33 and thence over the upper front contact of relay 329, through resistor 33|, over the front contacts of the RVZ relay 323 and thence through resistor 322 to ground. The potential now derived `from this potential divider and applied over the lower back contact of the CA relay 300 is increased so that the readings of the hydraulic pressure indicators 3M and l ill will now increase to 1,030 pounds per square inch rep resentative of the building up of the pressure in the landing gear control valve of an actual airplane after the pistons of the landing gear cylinders have moved to the limit of their movements in the retracting direction and before the kickout detent of the valve operates to permit the restoration of the valve stem and control lever to their neutral positions. Relay 329 upon operating also establishes a circuit from ground over its lower contacts and through the winding of the RV (relier` valve) relay 332 to battery and such relay operates.

In the trainer the pressure operated kick-out detent of the control valve is simulated by the detent |30 controlled by the solenoid |36 the circuit of which is opened upon the release of relay 321. When the solenoid releases, the valve stem |23 is released and through the action of the spring |43, roller |44 and cam |45 the control lever |25 is returned to its neutral position thereby opening thecontacts 3| to release the GU relay `324 followed by the release of the KGU relay 329 and the RV relay 332. A potential divider circuit is now established fromv battery through resistor |06, over the upper contacts of relay |0 I over conductor |01, over the iront contact of relay 323 and through resistor 322 to ground whereby the potential now derived from such potential divider and applied over the lower back contact of relay 300 to the indicators 3|4 and |54 causes the readings of such indicators to decrease to a value of 50 pounds per square inch as would result from the restoration of the control valve to its neutral position and the reestablishment of the open-center portion of the hydraulic system from the engine driven pump to the uid reservoir.

If for any reason the valve stem does not restore to normal, the hydraulic pressure continues to increase until the relief valve operates (1,250 pounds per square inch). This is simulated as follows: Relay 329 upon operating also established the circuit previously traced through the winding of the RV (relief valve) relay 332 to battery which relay, upon operating, opens the circuit of the RVI relay 333. Relay 333, which is also slow to release, releases after an interval and opens the circuit of the RVZ relay 323 which is slow to release. After an interval (during which the valve stem would normally return to its neutral position) relay 323 opens at its front contact the circuit over which the potential divider including resistors |31, 33| and 322 was established and closes a circuit through resistors |31 and 322. Thus the potential which established the kick-out pressure readings of 1,040 pounds per square inch on the hydraulic pressure indicators is changed to a value .which causes an indication of a pressure of 1,250 pounds per square inch.

The retraction of the landing gear when the electric motor driven pump is being used is simulated in the manner just described, the HP and HPI relays |0| and |34 being operated under the control of the EP relay |00 rather than under the control of the ENG relay |00. .i

To simulate the retraction of the landing gear by hand pump operation the landing gear selector lever |25 must be in the up position, the Main Hydraulic key |02 at the instructors desk must be in the closed position, the forward valve 2|6 must be closed and the aft valve 2|1 must be opened. Under this condition the FV and AV relays |20 and |2| are unoperated. When the hand pump handle 2 I3 is now operated relays i |1 and l i8 are alternately operated resulting in the intermediate operation and release of the I-IP relay |0| in the manner previously described. Relay |0| upon operating causes the operation of the IlP| relay |33 which locks, as previously v'"5 described, under the control ol' vthe GU relay 324 which operated in response to the operation of the selector lever |25 into its up position. With relay 324 operated the DGU relay 32'! operates and the pressure readings of the hydraulic indicators Il@ and 3|4 increase to 800 pounds per square inch as previously described. With relay 32] now operated the previously traced circuit for short-circuiting the right shaded pole winding 4|4 of the motor 4|5 oi the landing gear l2 potential divider circuit will now be established from battery, through resistor |31 over the lower contacts of the HP! relay |34, over conductor E33, over the upper back contacts of the GDF and KGD relays 338 and 339, over the inner uprnotor unit is reestablished from ground over 5g;

the inner lower front contact of the HP relay IBI. Since, however, relay |3| operates and releases in response to the strokes of the hand pump handle the motor M5 will operate intermittently in a direction representative of the f landing gear retraction. After the operation of the LG-LI limit switch the circuits function as described for the regular or auxiliary hydraulic system operation except that the HP and HPI relays lill and |34 release after the landing gear i has been retracted and the hand pump operation ceases. Relay lill upon releasingr will open the potential divider circuit from which potential is applied to the hydraulic pressure indicators |I4 and 3| so that such indicators will c now show zero pressure in the open-center portion of the hydraulic system.

Landing gear operation-Lowering operate as previously described and if the simulated landing gear is in its fully retracted position the Li relay 4I2 will be operated and consequently following the operation of relay 324 the KGU relay will operate and in the manner previously described the potential. divider circuit including resistors |3|, 533i` and 322 will be established whereby the potential derived therefrom and applied to 'the hydraulic pressure indica-tors |I4 and 3|4 will cause their readings to increase to the kick-out pressure of 1,040 pounds per square inch until the RVZ relay 323 is released in the manner previously described. When relay 323- releases a new potential divider circuit is established from battery through resistor |31 over the lower contacts of the HPI relay |34, conductor |33, the back contact of vthe RV2 relay 323 and through resistor 322 to ground and the potential derived from such potential divider and applied to the hydraulic pressure indicators ||4 and 3|4 will cause such indicators to show an increase in pressure to 1,250 pounds per square inch.

To lower the landing gear while in flight, vthe landing gear control lever |25 is moved to the down position thereby closing the cam operated contacts |45:` and establishing a circuit from ground .thereover, over conductor |41 and through the winding of the GD relay 334 to battery. Relay 334 upon` operating establishes a circuit from ground over its middle upper contacts and conductor 335 for the Landing Gear Selector Down lamp |48 to inform the instructor that the pilot has operated the landing gear selector lever |25 into its down position, and establishes the circuit of the DGD relay 333 which may be traced from ground over the middle lower contacts of relay 334, over the lower back contact of the L2 relay 331 and through the winding oi the DGD relay 336 to battery. If the hydraulic system has not been disabled, a

Eil

per contacts of the DGD relay 33B, through resistor 343, over the front contacts of the RVZ relay 323 and through resistor 322 to ground, from which potential divider a potential is derived and applied to the hydraulic pressure indicators H4 and 3|4, causing them to show a hydraulic pressure of 400 pounds per square inch which is the operating pressure required to lower the landing gear.

Relay 333 upon operating establishes an obvious circuit for the DGDi relay 313| which operates and establishes a shunt for the left shaded pole winding 423 of the motor 4|5 of the landing gear motor unit. This shunt circuit may be traced from ground over the inner lower contacts of the HP relay lili, over the upper back contacts of the FD and FU relays |39 and |40, over conductor Mi, over the inner upper back contact of the GDF relay 333, over the upper contacts of the DGDS relay 34d, over conductor 343 and through the left shaded pole winding 423 or" the motor 4 i 5. The motor now operates in a direction representative of the lowering of the landing gear. Relay 333 also closes the circuit of the MGD relay 344 which extends from ground over the contacts of the LG-L3 limit switch of the landing gear motor unit, over conductor 429, over the lower` contacts of relay 336 and through the winding ci relay 344 to battery, and relay 344 operates.

When the cam 424 closes the contacts of limit switch IgG-L2 as the slider of potentiometer LG? approaches the No. 3 terminals of the potentiernster winding, a circuit is established from ground thereover, over conductor 425 and through the winding of the L2 relay 337 to battery. Relay 337 upon operating connects ground over its upper contacts to control conductors 423 and 42l. Thus with conductors 426 and 421 extending through cable 422 connected to ground, the Landing Wheel Flap Indicators 342 and |42 are controlled to indicate the movement of the landing gear toward its down position. When the shaft si? of the landing gear motor unit reaches aA position representative of the start of the main landing gear in its lowering movement, cam 425i opens the circuit of the MGD relay 344 which now releases and connects ground over its lower contacts and the lower contacts of the DGDi relay 34| to control conductor 423 extending through cable 422 to the indicators 342 and closes the circuit for the KGD relay 339. Relay 333 upon releasing releases relay 34| and opens the shunt circuit of the left shaded pole winding 423 or" the motor H5 whereupon the motor cornes to rest.

Relay 333 is slow to release and therefore does not open the potential divider circuit previously traced through resistors |31, 34B and 322 until after relay 339 has operated to establish the poten-tial divider circuit extending from battery through resistor |33 to conductor |38 and thence over the upper back contact of the GDF relay the upper iront contact of relay 333, through resistor 345, over the front contact of RV2 relay 32S and thence through resistor 322 to ground. The potential now derived from this potential divider and applied to the hydraulic pressure indicators 3|4 and |I4 will cause such indicators to show readings of 850 pounds per square inch representative of the building up of the pressure in the landing gear control valve of an actual airplane after the pistons of the landing gear cylinders have moved to the limit of their movement in the lowering direction and before the kick-out detent of the valve operates to permit the restoration of the valve stem and control lever to their neutral positions.

As previously stated, the pressure operated kick-out detent of the control valve is simulated in the trainer by the detent |35 controlled by the solenoid |36, the circuit of which extends over conductor 328 and to ground over the upper contacts of the DGD relay 336. This circuit is opened upon the release of relay 336. When the control valve stem restores to its neutral position under the control of spring |43, roller |44 and cam |45, the switch |46 is opened thereby releasing the GD relay 334, followed by the release of the KGD relay 339 and the RV relay 332. A potential divider circuit previously traced through resistors IIB'B and 322 is again established whereby the potential derived therefrom and applied to the hydraulic pressure indicators 3|4 and ||4 causes the readings of such indicators to decrease to a value of 50 pounds per square inch.

The lowering of the landing gear when the electric motor driven pump is being used is simulated in the manner just described, the HP and HPI relays and |34 being operated under the control of the EP relay |09 rather than under the control of the ENG relay Illll.

To simulate the lowering of the landing gear by hand pump operation, the landing gear selector must be in the down position, the Main Hydraulic key |52 at the instructors desk must be in the closed position, the forward Valve 2|5 must be closed and the aft valve 2|'I must be opened. Under this condition the FV and AV relays |20 and |2| are both unoperated. When the hand pump handle 2 I 3 is now operated, vrelays ||`l and I I8 are alternately operated resulting in the intermittent operation and release of the HP relay Illl in the manner previously described. Relay |Il| upon operating causes the operation of the mi relay |34 which locks as previously described under the control of the GD relay 334, which operated in response to the operation of the selector valve lever |25 into its down position. With relays llI and |34 operated, the GD relay 336 operates and pressure readings of the hydraulic indicators ||4 and 3|4 increase to 400 pounds per square inch. With relay 336 now operated, the previously traced circuit for short-circuiting the left shaded pole winding 423 of motor M5 of the landing gear motor unit is established from ground over the inner lower front contact of the HP relay Ill I. Since relay ||l| operates and releases in response to the strokes of the hand pump handle, the motor 4|5 will operate intermittently in a direction representing the landing gear lowering. After the operation of the LG-L2 limit switch, the circuits function as described for the regular or auxiliary hydraulic system operation except that the HP and HPI relays |0| and |34 release after the landing gear has been lowered and the hand pump operation ceases, and relay upon releasing will open the potential divider circuit from which potential isapplied to the hydraulic pressure indicators ||4 and 3|4 so that such indicators will show zero pressure readings of the 'pressure in the open-center portion of the hydraulic system.

The instructor may prevent the lowering of the landing gear by operating the Landing Gear key |49 thereby establishing a circuit from ground over its contacts, over conductor l5!) and through the winding of the GDF relay 333 thus preventing the completion of the previously traced potential divider circuits from which potentials were derived for causing the hydraulic pressure indicators |4 and 3|4 to show a build-up of pressure above 50 pounds per square inch. Relay 338'also preventsA the establishment of the previously traced circuit for causing the motor M5 to operate. Solenoid |36 remains operated under this condition to lock the landing gear selector lever |25 in its down position. Under this condition the pilot would have to use the emergency hand crank to lower the landing gear.

A mechanical system for lowering the main landing gear is installed in the airplane to be used in the event offailure of the normal or auxiliary hydraulic'systems. This mechanism is controlled by a hand crank and drum mounted on the right wing spar at the center line of the airplane. In the trainer, this is simulated by the Emergency Landing Hand Crank key 34|:` at the instructors desk. When the pilot has to resort to the hand crank he can simulate the lowering of the landing gear mechanically by asking the instructor to operate key 346 to its down position thereby eS- tablishing a circuit from ground thereover, over the upper iront contact oi the GDF relay 338, which will be operated, over the upper contacts of relay 34| and conductor 343 and through the left shaded pole winding 423 of motor M5 to ground. The motor 4 5 will now operate in a direction representative of the lowering of the landing gear until the limit switch LG-L2 causes the operation of the L2 relay 331 and the release of the DGD and DGD! relays 336 and 34| as previously described. The release of relay 34| opens the short circuit of the winding 423 of the motor M5 to stop the motor. i

Wing flaps operation- Lowering To simulate the lowering of the wing flaps the pilot moves the lever |5| of the wing flaps selector valve to the left thereby closing the contacts at |52 to establish the circuit of the FD relay |33. Relay |39 upon operating establishes over its inner lower contacts a circuit extending over conductor |53 for the Flaps Selector Down lamp 341 at the instructors desk to inform the instructor that the pilot has operated the aps selector to its down position. At its middle upper contacts relay |39 establishes the circuit of the DFD relay 348 if the air speed of the simulated flight is less than knots and the HAS relay 349has not operated. This circuit may be traced from ground over the middle upper contacts of relay |39, over conductor |54, over the middle lower bank contact of relay 343, over conductor 355, over the normal contacts of the F-L2 limit switch of the flaps motor unit of Fig. 4, over conductor 35| and through the winding of relay 3113 to battery. At its middle lower contacts relay |39 establishes a locking circuit for the HPl relay i345 which may be traced from battery through the winding and upper contacts of relay |34, over the'upper con-` tacts of key Ill2 at the instructors desk and over the contacts of relay |33 to ground to prevent the release of relay |34 during the time that the wing flaps selector is in the downl position eX- cept through the operation oi the disable key |02 by the instructor.

Relay 348 upon operating establishes a circuit from ground over its upper contacts, over conductor 352 and through the winding of solenoid |55 which operates to position the locking detent |53 of the hydraulic valve |51 to lock the valve stem |58 in the operated down position. r Relay 348 also establishes a circuit from battery through resistor |31, over the lower contacts of the HPI relay |34, over conductor |38, over the upper back contact of the FDF relay 353, over the upper back contact of the KFD relay 354, over the inner upper contacts of relay 348, through resistor 355, over the iront contact of the RVZ relay 323 and through resistor 322 to ground. Potential derived from this potential divider is applied to the hydraulic pressure indicators ||4 and 3|4 whereupon such indicators are operated to show pressure readings of 300 pounds per square inch representative of the pressure which would be applied from the open center system of an actual airplane to the wing naps operating cylinders to lower the wing flaps.

Relay 348 also establishes a circuit from ground over the inner lower front contacts of the HP relay i (ll, over conductor IE5, over the lower back contacts of relays 334, 324 and 349, over the inner upper back contact of relay 353, over conductor 353, over the lower back contact of the FU relay |43, over conductor |59, over the lower contacts of relay 348, conductor 351, and through the right shaded pole winding 430 of motor 43| of the flaps motor unit to ground. Since the stator winding 432 of this motor is energized from the alternating current source 435, the motor now turns the shaft 433 and through the gears 434 and 435 turns the sliders of the telemetric transmitters FT and FT in a direction representative of the lowering ci the wing aps. These transmitters control the Landing Wheel Flap Indicators |42 and |43 on the pilots and instructors instrument panels in the well-known manner to indicate the lowering of the wing flaps.

When the cam 436 operates the contacts of limit switch F-L2 to their alternate position as the shaft 433 approaches a position representative of the lowered positions of the wing flaps, a circuit is established from ground applied as previously described to conductor 35|), thence over the alternate contacts of the F-LZ limit switch over conductor 431, and through the winding of the KFD relay 354 to battery. At the same time the previously traced circuit for the DFD relay 343 is opened and relay 343, upon releasing, opens the shunt of the right shaded pole winding 438 of the motor 43| thereby stopping the motor.

Relay 348 is slow to release and therefore does not open the potential divider circuit previously traced through resistors |31, 355 and 322 until after relay 354 has operated to establish the potential divider circuit extending as previously described from battery through resistor |31 to conductor |38 and thence over the upper back contact of relay 353, over the upper front contact of relay 354, through resistor 358, over the front contact of the RVZ relay 323 and thence through resistor 322 to ground. The potential now derived from thisy potential divider and applied to the hydraulic pressure indicators 3M and |I4 is increased so that the readings of the indicators will increase to 460 pounds per square inch representative of the building up of the pressure in the wing naps control valve of an actual airplane after the pistons of the wing iiaps cylinders have moved to the limit of their travel 1n the lowering direction-and before the kick-out detent of the valve operates to permit the restoration of the'valve stern and control lever to their neutral positions.

The pressure operated kick-out detent of the control valve is simulated in the trainer by the detent I 53 controlled by the solenoid |55, the circuit of which is opened when the DFD relay 343 releases as previously described. When the control valve stern restores to its neutral position under the control of spring |39, roller |6| and cam |52, the switch |52 is opened thereby releasing the FD relay |39 followed by the release of the KPD relay 354 and the RV relay 332. A potential divider circuit previously traced through resistors |33 and 322 is'again established whereby the potential derived therefrom and applied to the hydraulic pressure indicators 3| 4 and H4 causes the readings of such indicators to decrease to a value of 50 pounds per square inch.

The lowering of the wing flaps when the electric motor'driven pump is being used is simulated in the manner just described, the HP and HP! relays |0| and |34 being operated under the control of the EP relay H39 rather than under the control of the ENG relay |80.

To simulate the lowering of the wing flaps by hand pump operation, the wing naps selective 'valve must be in the down position, the Main Hydraulic key |512 at the instructors desk must be in the closed position, the forward valve 2|6 must be open and the aft valve 2H must be closed. Under this condition relays I2@ and |2| will both be unoperated. When the hand pump handle is now operated, relays ll'l and H8 are alternately operated resulting in the intermittent operation and release of the HP relay |0| in the manner previously described, Relay It! upon operating causes the operation of the HPI relay |34 which locks as previously described under the control of the FD relay |39, which operated in response to the operation of the selector valve stein |53 into its "doi/vn position. With relays lil! and |34 operated the DFD' relay 348 operates and pressure readings of the hydraulic indicators H4 and 3|4 are increased to 300 pounds per square inch as previously described. With relay 343 now operated the previously traced circuit lor short-circuiting the right shaded pole winding 43|? of motor 43l of the wing liaps motor unit is established from ground over the inner lower contacts of relay Il. Since relay IBI opcrates and releases in response to the strokes of the hand pump handle, the motor 43| will operate intermittently in a direction representative of the lowering of the wing flaps. After the operation of the F--LZ limit switch, the circuits function as previously described for the regular or auxiliary system operation except that the HP and HPl relays iii! and |34 release after the wing flaps have been lowered and the hand pump operation ceases and relay upon releasing will open the potential divider circuit from which potential is applied to the hydraulic pressure indicators ||4 and 3|4 so that such indicators will now show zero readings of pressure in the open-center portion of the hydraulic system.

If both the regular and auxiliary hydraulic systems of the airplane have become disabled, the pilot may lower the wing iiaps by direct hand pump operation by operating the wing aps selector lever into its down position, by clos- )upper back contacts of relay 353. contacts relay 353 supplies ground from the lower .contacts of relay |39, over conductor |66, over 'the lower contacts of relay 353 and conductor 352, through the solenoid |55 to prevent the re- 4ing thel forward emergency flap lowering valve and by opening the aft emergency flap lowering valve. In the trainer these operations are simu- "lated by the similar operation of the wing flaps selector lever |5| and theforwarcl and aft valves 2|6 'and 2|1. Under these conditions the FD relay |39, the DFD relay 348 and the FV and AV relays and |2| will be operated. Relays |20 and |2| upon operating-close obvious circuits for lthe forward and aft lamps |63 and |64 at the instructors desk to informV the instructor that the valves have been operated to positions to allow the direct operation of the wing flaps by hand pump operation.

With relays |20, |2| and 348 operated, upon winding 430 of motor 43|of the ilaps motor unit to ground. The result is an intermittent operation of the motorf in a direction representative of the lowering oi?l the wing aps. When the shaft 433 has rotated to aposition representative of the lowered position of the wing flaps, cam

' 436 operates the'contacts of limit switch FL-Z to open the circuit of relay 348 which releases and `stops the motor 43|. the circuit of the solenoidI |55 is opened and the When relay 348 releases,

-lever |5| of the flaps selector returns to its neutral position. Since direct hand pump operation `of the wing flaps does not build up pressure in the open-center portion-oi the hydraulic lsystem of 'an airplane, the hydraulic pressure indicators remain at zero pressure. In the trainer this is simulated since with the HP and HPI relays |0| and |34 unoperated, no potential divider cir-f cuits are established as previously described 'from which potential for operating the indicators may be derived.

The simulation of the disabling of the wing -aps may be simulated without simulating the disabling of the main hydraulic line by the operation of the Flaps Selector key 359 at the instructors desk, therebyV causing the operation of the FDF relay 353 over an obvious circuit. With relay 353 operated, the potential divider circuits previously traced from which potentials were derived to cause the hydraulic pressure indicators ||4 and 3|4 to show the -operating and kick-out pressures of 300 and li6() pounds per square inch cannot be established and n,the normal path by vwhich the motor 43| of the flaps motor unit was controlled by relay 340 .is opened at the inner At its lower lease of such solenoid'and the removal of the detent |56 of the valve |51. The lever |5| thus remains locked in its down position. With this type of failure the flaps can be lowered by direct hand pump operation as previously described.

Wing flaps operation-Raising lay |40. Relay |40, upon operating, establishes "over'its inner lower contacts-the circuit extending over conductor |66 for the Flaps Selector Up lamp 351 at the instructors desk to inform the instructor that the pilot has operated the flaps selector to its up position. At its upper contacts, relay |40 establishes a circuit from ground over conductor |69, over the normal contacts of limit switch F-LI of the flaps motor unit, over conductor 438 and through the winding of the DFU relay 360 to battery. At its'lower contacts, relay |40 establishes a locking circuit for the HPI relay |34 which may be traced from battery through the winding and upper contacts of relay |34, over the upper contacts of key |02 at the instructors desk and over the contacts of relay |40 to ground to prevent the release of relay |34 during the time that'the wing'aps selector is in the up position, except through the `operation of the disable key |02 by the instructor.

Relay 360, upon operating, establishes a circuit from ground over itsupper contacts and conductor 352 through the winding of solenoid |55 which operates to position the locking detent |56 of the hydraulic valve |51 to lock the valve stem |58 in its operated up position. Relay 360 also establishes a circuit from battery through resistor |31 over the lower contacts of the HPI relay |34, over conductor |36, over the upper back contact of the HAS relay 349, over the upper back Contact of the KFU relay 36 over the upper inner contacts of relay 360, through resistor 362,` over the front Contact of the RVZ relay 323, and through resistor 322 to ground. Potential derived from this potential divider is applied to the hydraulic pressure indicators ||4 and 3|4 whereupon such indicators are operated to show pressure readings of 550 pounds per square inch representative of the pressure which wouldbe applied from the open-center system of an airplane to the wing flaps operating cylinders to raise the wing flaps.

Relay 360 also establishes a circuit from' ground over the inner lower front contact of the HP relay |0I, over conductor |65, over the lower back contacts of relays 334, 324 and 349, over the lower contacts of relay 360 andv over conductor 363 through the left shaded pole winding 439 of motor 43| of the flaps motor unit to ground. Since the stator winding'432 of this motor is energized from the alternating current source 405, the motor now turns the shaft 433 in a direction 'representative of the raising of the wing aps and the telemetric transmitters FT and FT accordingly control the indicators |42 and 342 respectively.

When thecam 440 operates the contacts of limit switch F-LI totheirjalternate position, as the shaft 433 approaches 'a positionl representative rof the raised positions of the wing flaps, a circuit is established from ground applied as previously described to conductor |69, thence over the alternate contacts of switchF-LL over conductor 44|, over the inner upper back contact of the HAS relay 349 and to battery through the winding of the KFU relay 36|. `At the same time, the previously traced circuit for the DFU relay 360 is opened and relay 360 upon releasing opens the shunt of the left shaded pole winding 439 of motor 43| thereby stopping the motor.

Relay 360 is slow to release and therefore does not open the potential divider circuit previously traced through' resistors |31','36 2'`and 322 until after relayv 36| has operated to` establish the Vpotential divider circuit extending as previously traced from battery through resistor |31A to conductor |30 and thence over the upper back contact of the HAS relay 349, over the upper front contact of relay 33|, thence through resistor 365, over the iront contacts cf the RVZ relay 323 and through resistor 322 tol ground. The potential now derived from this potential divider and applied over the lower back contact of relay 399, is increased' so that the readings of the hydraulic pressure indicators 3|4 and ||4 will increase to 750v pounds per square inch, representative of the building up of the pressure in the wing flaps control valve oi" an actual airplane after the pistons of the wing iiaps operating cylinders move to the limit of their travel in the raising direction and before the kick-out detent of the valve operates to permit the restoration of the valve stem and control lever to their neutral positions.

The pressure operated kick-out detent of the control valve is simulated in the trainer by the detent |56 controlled by the solenoid |55 and is released when the DFU relay 369 releases as previously described. When the control valve stein |58 restores to its neutral position under the control of spring |60, roller |6| and cam |62, switch |61 is opened thereby releasing the FU relay |49 followed by the release of the KFU relay 36| and the RV relay 332. A potential divider circuit previously traced through resistors |96 and 322 is againY established whereby the potential derived therefrom and applied to the hydraulic pressure indicators 3 |4 and |4 causes the readings of such indicators to decrease to a value of 50y pounds per square inch.

Raising of the wing flaps when the electric motor driven pump is being used is simulated in the lmanner just described, the Hl? and HP'i relays IM and |34 being operated under the control of the EP relay |09 rather than under the control of the ENG relay |90.

To simulate the raising of the wing flaps by hand pump operation, the wing flaps selector lever must be in the up position, the Main Hydraulic key |92 at the instructors desk must be in the closed position, the forward valve 'ZIB must be open and the aft valve 2|'| must be closed. Under this condition relays |23 and |2| will both be unoperated. When the hand pump handle is now operated, relays and H8 will operate .alternately resulting in the intermittent operation and release of the HP relay lill in the manner previously described. Relay im upon operating causes the operation of the HPI relay |134 which locksA as previously described under the control of the FU relay |49 which operated in response to the operation of the selector valve lever |5| into its up position. With relays i9| and |34 operated the DF'U relay 369 operates and the pressure readings of the hydraulic indicators H4 and 3|4 are increased to 550 pounds per square inchas previously described. With relay 369- now operated, the previously traced circuit for controlling the motor 43| of the wing 4flaps motor unit is established from ground at the inner lower contacts of relay ||l|. Since relay ||l| operates and releases in response to the strokes of the hand pump handle the motor 43| will operate intermittently in a direction representative of the raising of the wing naps. After the operation of the F-Ll limit switch, the circuits function as described for the regular or auxiliary system except that the HP and HPl relays ||l| and |34 release after the wing flaps have been raised and hand pump operation ceases and relay |9| upon releasing will open the potential divider from whichpotential is applied to the hydraulic pressure indicators ||4 and 3|4 so that such indicators will show zero readings of pressure in the open-center portion of the hydraulic system.

If the air speed is in excess of knots the wing flaps may not be lowered but if they are in the process of lowering, they are automatically raised. This is simulated in the trainer by the operation of the high air speed (HAS) relay 349 over a circuit established from groundY over contacts of the L3 limit switch of the indicated air speed motor unit of Fig. 2, closed by the cam 249 when an air speed in excess of 135 knots is simulated, over conductor 22|] and through the winding of relay 349 to battery. When` relay 349 operates if the naps are up, the circuit of the DFD relay 348 cannot be closed by the operation of the FD relay under the control of the flaps selector lever |5| because its circuit is opened at the middle lower back contact of relay 349and consequently the simulation of the lowering of the wing naps cannot be made. If the flaps are down, the operation of relay 349 willestablish the circuit of the DFU relay 36|] from groundover the inner lower contacts of relay 349, over conductor |69, over the normal contacts of the F-LI limit switch of the wing flaps motor unit, over conductor 438 and through the winding of relay 399 to battery, or if the wing flaps are in the process of lowering, relay 349 will open the circuit of the DFU'relay 348 at its middle lower back contact and will establish the circuit of relay 33|) as just described. The release of relay 348 will stop the rotation of the motor 43|- in the lowering direction and the operation of relay 399 will establish a circuit iromground over' the lower contacts of relay 349, over the lower contacts of relay 360, conductor 363 and through the left shaded pole winding 439 of the motor 43| whereupon the motor will operate in a direction representative of raising the wing flaps until the cam 449 operates the limit switch FL-i to open the previously traced circuit of relay 360 to stop the motor. Relay 349 also opens at its upper back contact the potential divider circuit which would ordinarily be established as previously described to cause the hydraulic pressure indicators |'|'4 and 3 I4 to show pressure readings. These operations simulate the movement of the wing flaps of anactual airplane to their raised positions due to the slip stream when the air speed is above 135 knots in which case no hydraulic pressure would be used and consequently no hydraulic pressure readings would be indicated by the pressure indicators.

In the actual airplane since the hydraulic valves which control the landing gear' and the Wing iiaps mechanisms are positioned in tandem relationship in the open-center system, the operation of the wing flaps control valve prevents ther application of the full hydraulic pressure to the landing gear operating cylinders. rThis prevents the simultaneous operation of both the wing naps and the landing gear. This is simulated in the trainer by extending the circuits established over the lower contacts of the DF and DFD relays'SB and 34S which control the motor 43|v of the wing naps motor unit, over the lower contacts of the GD and'GU relays 334 and 324 so that if either of these relays is operated in response to the operation of the landing gear selector valve lever |25, the motor 43| cannot be operated to simulate the operation of the wing flaps. Also the circuit established over the lower contacts of the,` DGU relay 321 and the upper contactsof the DGD| relay 34| which control the motor 4|5 of a landing gear motor unit, are ex-y tended over conductor |4|fand`over back contacts of the FU and FD relays |40' and |39 so that if either of these relays is operated in response to the operation of the wing flaps selector valve lever |5I, the motor 4|5 cannotbe operated l to simulate the operation of the landing gear. Neither motor can therefore operate if the selector valves are simultaneously operated.

Brake pedal operation The brakes of the actual airplaneV are operated by hydraulic pressure supplied from the accumullators of the constant pressure portion of the hydraulic system as previouslyl described. Noru mally this pressure is kept at about 1100 pounds 7i Aper square inch. In the trainer the operation of either brake pedal will cause the operation of the BK relay |10. It will be assumed that the right foot brake pedal is operated thereby rotating the shaft 22| to rotate cams 222 and 223 and through the gear sectors 224 and 2.25 and pinions 225 and 221y to rotate the sliders of poten tiometers RBI and HB2 toward the No. 3 terminals of the potentiometer windings.

223 are provided to control the flight circuits of the trainerv and do not perform any direct `functions with respect to the present invention.

The operation of the switch N of the right brake assembly to itsY alternatel position establishes a circuit from ground over the normal contacts of the N switch associated with the left brake assembly, over the alternate contacts of the N switch associated with the right brake assembly,

. over conductor 220 and through the winding of the BK relay to battery. Similiarly the operation of the left brake pedal would cause the operation of the N switch associated therewith to its alternate position thereby 'connecting ground to conductor 228 to complete the circuit" of relay |10 or if both brakes are operated simultaneously= relay |10 will operate. j

Relay |10 upon operating opens the normally iso These potentiometers and the switch operated by cam` closed cir-cuit of the BPD relay |1| which releases and closes the circuit of the Foot Brake lamp |12 at the instructors desk to inform the conductor l14 and to the junction point between resistor 409 and the winding lof potentiometer i BPH] associated with the brakepressure'motor" unit, whereby the potential applied from the slider of the potentiometer over conductor 4H, over the back contact of relay 30| to the brake pressure indicators 304, 305, |04 and |05 becomes,

reduced representative of the temporary drain-"I` of pressure from the accumulators of an airplane to operate the brakes. As soon as relay |1| is fully released, the circuit through resistorl |13 Should neither the engine driven pump or the velectric motor driven pump be operating when the brakes are applied,v this conditionI will be simulated in the trainer by the rele'asedcondition of the ENG and EP relays|00 and |03. `Under ,Q this condition eachtimeuthat thefbrake pedal,

, is opened and the potential applied to the pressure indicators again rises representative of the restoration of pressure in the accumulators due to the continued operation of the engine driven y or electric motor driven pump.A

.pressure in the accumulators.

22 voperate and release and being slow to release will establish a circuit from ground over the normal contacts of the N switches associated with the brake assemblies, over conductor y229, over the lower contacts of relay |10, over the lower back contacts o-f relays |09 and |00, over conductor |15, over the upper back contact of the AE relay 30|, over conductor 443 and through the left shaded pole Winding 444 of the motor 403 of the brake pressure motor unit. This circuit is closed only during the releasing time of relay |10 and causes the motor 403 to momentarily turn in a direction representative of a reduction in The motor 403 turns the slider of potentiometer BC|0 a short distance toward the No. 3 terminal of the potentiometer winding thereby reducing the potential applied therefrom to the brake pressure indi- "cators 304, 305, |04 and |05 whose readings are then decreased to show the drain of pressure incident to the operation of the brakes.

Continued operation and release of the brakes under this condition will result in a gradual bleeding of the pressure from the accumulators which is simulated by the gradual movement of the slider of potentiometer BP|0 towards the No. l'terminal of the potentiometer winding and the gradual decrease in the pressure readings of the brake pressure indicators to 600 pounds per square inch, at which time the slider will be at the No. 1 terminal of the potentiometer Winding. When the slider has thus moved, the cam '44'5 closes. the contacts of the BP-Ll limit switch thereby establishing a circuit from ground thereover and over conductor 440 through the winding of the accumulator empty (AE) relay 30| to battery.

Relay 30| upon operating opens the shunt circuit for theleft shaded pole winding 444 of the motor 403 and at its lower front contact connects ground through resistor 355 and through resistor 302 to the brake pressure indicators 304, 305,

|04 andl l0'5 whereby the indicators are controlled to readv zero representative of the complete zero pressure condition of the accumulatore. i

Brake pressure can, however, be maintained in the accumulators of the airplane by the operation of the hand pump. In the trainer, this is simulated by the intermittent closure of the circuit of the CA relay 300 by relays l l1 and i I8 under. the control of the hand pump switch 2l2, which circuit extends from ground over the inner upper contacts of relays i8, l l1 and 20, overc-onductor |03, over the contacts of the BP-LZ limit switch,

which will be closed until a simulated accumujlator pressure of 1100 pounds has been estab- 1 lished, thence over conductor 400 and through the v'winding of relay 300 to battery. Relay 300 upon each energization will establish the previously traced shunt circuit for the right shaded pole winding 402 of motor 403 so that the motor' will turn in a directi'onto advance the slider 'of potentiometer BP|0 towards the No. 3 terminal of its winding, representative of the small increase (l5v in the pressure in the accumulators which would result from .the hand pump operation. If the drain of pressure due to the operation of the .jbrakesis less than the building up of pressure by the hand pump operation, the sum of the incre- 70.

ments of movement of the motor 403 in the direction representative. of increased accumulator .pressure as controlled by the response of relay 300 to hand pump operation, will be greater than the y z sum ofthe increments of movementof the motor is depressed and then released, relay |10 will v75Min the Iopposite Idirection under the control of aeree 23 the BK relay Il!) and therefore the potential applied from the slider of potentiometer BP-IB will cause the brake pressure indicators to show a gradual increase in pressure,

The operation of the parking brake at the pilots pedestal closes the contacts of switch ll to light the Park Brake lamp lll' at the instructors desk but has no effect on the simulated'hydraulic system since in the actual airplane the parking brake merely serves to lock the foot brake pedals in their operated positions if they have been operated.

What is claimed is:

1. In a ground trainer for aircraft flight personnel, means for simulating the operation of the engine driven pump of an airplane, a, simulated hydraulic pressure indicator, a source of current, a relay .operable in response to said engine driven pump simulating means for connecting said source of current to said indicator to cause said indicator to show a pressure reading .representative of the operation of the engine vdriven pump, means for simulating the operation of a hydraulically operable device, a relay for controlling said latter means, a control operable by a pilot for operating said latter relay, and means controlled by said latter relay for varying the `current applied to said indicator wherby said indicator is caused to show a cha-nge in hydraulic :pressure comparable to the change in pressure incident to the operation of said device.

2. In a, ground trainer for aircraft flight personnel, means for simulating the operation of the engine driven pump of an airplane, a simulated hydraulic pressure indicator, a source .of current, a relay operable in response to said engine driven pump simulating means for applying ra potential from said source to said indicator to .cause said indicator to show a pressure reading representative `of the application of pressure from the engine driven pump to theopen-center hydraulic system of an airplane, means for simulating the operation of a hydraulically operable device, a relay for controlling said latter means, a control operable by a, pilot for operating said ,latter relay, and means controlled by said rlatter lrelay for increasing the potential applied to said indicator from said source whereby said indicator is caused to show-an increased vreading representative of the increase of hydraulic vpressure in the open-center system of an airplane incident to the operation of a control valve thereof.

3. In a, ground trainer foraircraft flight personnel, means for simulatingthe operation of the hydraulic vpressure pump of an airplane, asimulated hydraulic pressure indicator, a source of current, a relay operable in response to said f pump simulating means .for applying a potential from said source to said indicator to cause said indicator to show a, pressure .reading representative of the application of pressure from the pressure pump -to the open-center hydraulic system of an airplane, means for simulating vthe operation of a hydraulically operable device, a

relay for-controlling said latter means, a control operable by the pilot for operating said Vlatter relay, means .for locking said .control in its operated `position representative of the operation of .the hydraulically operated kick-out detent of the control valve of an airplane, means con- -trolled by said latter relay 'for increasing the .potential applied to said indicator from said source whereby said indicator is caused to show .an 4increased yreading representative of the increase of hydraulic pressure kin the `open-center system. of airplane incident to the operation of the control valige thereof, means operable upon the completion of the operation of the hydraulic device simulating means to further increase the pOtQIlal .applied from said source to said indicator representative of the building up of pressure in the control valve following the completion of the 'operation of the lhydraulic device controlled thereby to force out the detent of the valve, and means controlled by said latter means to release saidlocking means.

4.,.` In a ground trainer for aircraft flight personnel, means for simulating the operation of the hydraulic pressure pump of van airplane, a simulated hydraulic pressure indicator, a source of current, a, relay `operable in response to said pump simulating means for applying a potential yfrom said source to said indicator to cause said indicator to show .a pressure reading representative of the application of pressure from the pressure pump to the -open-center hydraulic system of `an airplane, means for simulating the operation of a hydraulically operable device, a control relay for controlling said latter means, a control operable by the pilot for operating said control relay, means for locking said Acontrol in its operated position representative of the hydraulically operated kick-out detent of the control valve of an airplane, means controlled by said latter rela-y for increasing the potential applied to said indicator from said source whereby said indicator is caused to show an increased reading representative of theincrease of hydraulic pressure in the open-center System of an airplane incident to the operation of the control valve thereof, means operable under the control of said control relay upon the completion of the operation of ,the .hydraulic device simulating means to -further increase the potential applied from Said source to ,said indicator representative of the building up of pressure in the control valve following the completion of the operation of the hydraulic device controlled thereby to force out the detent of the valve, means controlled by said latter means to release said locking means, means also controlled by said latter means to initiate the measurement of a predetermined time interval, and means effective if said locking means fails to release said control relay Within the predetermined interval to 'further increase the potential applied from said source to said indicator representative of the building up of pressure in the open-center system tothe point at which the relief valve of the open-center system opens.

5. In a ground trainer for aircraft flight personnel, vmeans for Vsimulating the operation 'of `the hydraulic Vpressure pump of an airplane, a simulated lhydraulic pressure indicator, a source of current, a relay operable in response to said pump simulating means for `applying a potential from said source to said indicator to cause said Vindicator to show a pressure lreading representative of the application of pressure from the pressure pump to theopen-center hydraulic system of an airplane, means for simulating the operation @La hydraulically operable device, a relay for controlling the latter means, a, control operable by a pilot for operating said latter relay, means for locking said control in its operated positionrepresentative of the operation of the hydraulically 'operated kick-out detent of the control' valve of an airplane, means controlled by said latterrelay for increasing the potential Aapplied to said indicator from said source whereby 25 Y reading. representative of the increase of hydraulic pressure in the open-center system of an airplane incident to the operation of the controlv indicator representative of the buildingv up of pressure in the control valve following the completion of the operation of the hydraulic device controlled thereby to force out the detent of the valve, means controlled by said latter means to release said locking means, and means effective upon the release of said control means to again apply said rst potential to said indicator to cause ysaid indicator to show a reduced pressure.

'6. In a ground trainer for aircraft flight personnel, means for simulating the operation of the. auxiliary motor driven pump of an airplane, means for simulatingthe operation of the engine driven pump of an airplane, a simulated hydraulic pressure indicator, a source of current, a relay operable in response to either of said simulating pump means for applying potential from said source to said indicator to cause said indicator to show a pressure reading representative'of the application of pressure from the engine driven pump or from the motor driven pump to the open-center hydraulic system of an airplane, means for simulating the operation of a hydraulically operable device, a relay for controlling said latter means, a control operable by a pilot for operating said latter relay, and means for increasing the potential applied to said indicator from said source whereby said indicator is caused to show a changed reading representative of the change of hydraulic pressure in the open-center system of an airplane incident to the operation of a control valve thereof.

7. In a ground trainer for aircraft flight personnel,` means for simulating the operation of the emergency hand pump of an airplane, a simulated hydraulic pressure indicator, a source of current, a relay intermittently operable in response to said pump simulating means vfor applying a potential from said source to said 'indicator representative of the application of pressure from said pump to the open-center hydraulic system of an airplane, means for simulating the operation of a hydraulically operable device, a relay for controlling said latter means, a control operable by a pilot for causing the intermittent operation of said latter relay in response to the operation of said first relay representative of the step-by-step manner in .which the hydraulically operated device of an airplane would 8. In a ground trainer` for aircraft flight per-v sonnel, means for simulatingthe operation o f the' auxiliary and engine driven pumps or an' airplane, a relay Ioperable in response Vto either of said pump simulating Ameans representative'- of the application of pressure from either the engine driven or auxiliary pump to' the open-center Lhy draulic system of an airplane, meansfor preventing the operationof said relay in simulation of the failure of the hydraulic system of an airplane, means4 for simulating the operation of the emergency hand pump of'anairplane, means for sim- 26K.. ulating the operation of' a' hydraulically operable device, a relay for enabling the operation of said latter means, a control operated by a lpilot for' sonnel, means for simulating the operation `of the auxiliary, engine driven and emergency hand pumps of an airplanameans for simulating the operation of thevohydraulically operable wing aps operating device cian airplane, a rst relay for' enabling the operation of said latter means, a

second relay'operable in response to any one of, said pump simulating means representative of the application oi hydraulic pressure from any onefof the pumps to the open-center hydraulic system of an airplane, acontrol operable Vby a pilot for operatingl said first relay whereby said device simulating means becomes operable under the control of said' second relay, means for simuof the wing ilaps operating device oi an airplane to lower the Wing ilaps against the pressure of the slip stream.

10. In a ground trainer for aircraft flight'personnel, means lfor simulating the operationr of the auxiliary, engine driven and emergency hand manner representative'of the lowering of the wing flaps, a second relay for enabling the operation of said latter means in a manner representative of the raising of the Wing flaps, a third relay operable in response to any one of said pump simulating means'representative of the application of hydraulic pressure from any one of the pumpstothe open-center hydraulic system of an airplane, a control operable by a pilot for operating either said first or said second relay whereby said device simulating means becomes operable under the control of said third relay, means for simulating the air speed of a simulated flight, and means effective if the simulated air speed 'of Va operation o'f'said second relay to thereby cause the operation of said device simulating means' in a manner representative of the raising *of` the wing flaps irrespective of the operated position of said control to simulate automatic movement off the wing flaps of an airplane to their raised` positions due to the pressure of the slip stream.

11`. In a ground trainer for aircraft ight per-y sonnel, means yfor simulating the operation of the auxiliaryl and engine driven pumps lof an airplane, means for simulating the operation of ,thel hydraulically operable devices of an airplane, first.` relays forenabling` the operation of one of saidA latter means, second relays for enabling the op-v eration of another of said latter means, a relay operable in response` to ,any one ofvsaid pump..

271|v simulating' means representative ofthe application of--hydraulic pressure from any one of the pumps, t'o the open-center hydraulic system of an'airplane, agflrst controloperable bya pilot for operating4 either one` of said. iirstrrelays whereby said one device simulating means becomes operatedqunder the control oil said latter relay, a second control operable by a pilot for operating either one of said. second relays whereby said other device simulating-meansv becomes operable under the control of said latter relay, and circuit meanseffective to prevent the operation of either of; said device simulating means ii said contrcls are simultaneously operated.

12.. Inga groundtrainer for aircraft flight personnel, means for simulating the operation of the auxiliary and engine driven pumps of an airplanesmeans for simulating the operation of the hydraulically: operable landing gear operating device of an airplane, first relays for enabling the Operation of. said'latter means, means for simulatingv the operation of, the hydraulically operable-wing flaps operating device of an airplane, second relays for enablingy the operation `of said latter device simulating means,` arelay operable in response to any one of said pump simulating meansrepresentative of the application of hydraulic pressure from any, one of the pumps-to the open-center hydraulic system of an airplane, a. firsti control. operable. bya pilot for operating either one of said rst relays whereby said. rirst device simulating means becomes operable under thecontrol of saidr latter relay, a second control operable by a pilot for operating either one of said second.. relays whereby said second device simulating means becomes operable under the control-of vsaid latter relay, and circuit means-effective to prevent the operation of either. of said device simulating means if one olf-said first relays and one of saidsecond relaysare simultaneously operated by the simultaneous operation of said controls`A 13. Inaground-trainer for aircraft flight personnel, means VAfor. simulatingY the operation ofthe auxiliary, engine driven and emergency hand pumps of anairplane, meansfor simulatingV the operation of the hydraulically operable device fory operating` the landinggear. ofan airplane, a relay,Y enabling. the operation of ysaid latter means in a. manner representative of1 the lowering of the landing gear, a relay operable in response to any one ofy said pumpsimulating means representative .of the applicationnfhydraulic pressureirom one of the pumps to the open-center` hydraulic systen'iAV of an airplane. a control operable by a pilotfor operating-said rst. relay whereby saiddevice simulating means becomes operable under the controlof said second relay,- means -for preventing. theoperation ofn said second relay in simulation of the failure of the hydraulic system of an airplane, and .means operable to control said device simulating. means independent of said secondfrelay in simulation ofthe mechanical. system providedin an airplane. for lowering-theland ing gear.

14. In .a ground trainer for. aircrafttiight personnel, .means for simulating the operation, of.

the auxiliary, enginedriven and .emergency hand pumps of an.A airplane, means for simulating the,

resentative ofthe application of hydraulic pressure from any oneof sad pumps to the opencenter. hydraulic systemof an. airplane, a control operable by a. pilot-for.r operating said rst relay whereby.- said device simulating means becomes operable under the control of'said second relay, andameans operable to transferthe control of said device simulatingr means. from said second relay' directlytn saiclemergency hand pump simpumpsof fan-airplane, means for simulating the 2U, Y

operation. of the hydraulically operable device for operatingy the.wing flaps of an airplane, a relay for enabling the operationcf said latter means in*v a manner representative of the lowering of the wing naps,` arelay operable irl-response to any one of saidpump simulatingl means representativeof the applicationof hydraulic pressure iromany one of` the pumps to the open-center hydraulic system ofA an airplane, a control oper- .able by4 a pilot for operating saidy rst relay whereby said devicesimulating means becomes operable under the controliof` said second relay, means operable to transferA the control of said device simulating meansfrom said. second` relay to said hand pump simulatingmeans, andmeans operable by4 thefpilot. for operating said lattermeans in s imulationof the operation of valves whereby the'hand pump of, an airplane is connected directly with thefwing apsoperating device of` an airplane whereby the wing flaps are lowered by direct hand pump operation when the Wingfflaps operating device fails to respond to pressure suppliedV thereto from the open-center hydraulic system.

16. In a-ground1trainer for aircraft flight peri sonnel, means for. simulating. the operation of the auxiliary, engineA drivenV andemergencyA hand pumps-of an airplane, means-.rior simulating the production ohydraulic. pressure, indicators for simulating the indication-of the hydraulic pressure in theconstant pressure accumulatore of an airplane, are-lay` operable in response to the operation of any one of said pump simulating means to control said pressure simulating means,

a a source ofcurrent, means controlled by said pressure, simulating meansy for deriving a potential iromsaid-sourceand applying it to said indicators.. and means controlled by said pressure simulating,meansA for causing the release of said relay andA the arrestingof. the operation of said pressure simulating meanswhen said indicators show pressuresofa predetermined value.

17. In a ground trainer ion aircraft ,flightpersonne-l, means for simulating,the-'operationof the l emergency hand pump-of anairplane, means for operationy of the hydraulically operable device 70 for operating the wing naps or an. airplane,.a

ingof the `wing flaps, a relay operable in response.

to any one of said pump simulating means repsimulating.` theproduction of hydraulic pressure, indicators for simulatingthe indication of the hydraulick pressure in. the constant: pressure vaccumulators ofan airplane, a relay intermittently operable. in.` response., to., the operation. of said hand pump simulating .means to` control the .intermittent .operationfof rsaidapressure4 simulating means, a sou-roept, currenty means-controlled vby, the intermittent `:operationlof said `pressure .simulatingmeans. for ,deny-maan. increasing potential from said'surce and"fr applying it to'said' asiesos indicators whereby said indicators are caused to show intermittently increasing readings, and means controlled by said pressure simulating means for causing the release of said relay and the arresting of the operation of said pressure simulating means when said indicators show pressures of a predetermined value.

18. In a ground trainer for aircraft flight personnel, means for simulating the operation of the auxiliary, engine driven and emergency hand pumps of an airplane, means for simulating the production of hydraulic pressure, an indicator for simulating the indication of the hydraulic pressure in the open-center portion of the hydraulic system of an airplane, indicators for simulating the indication of the hydraulic pressure in the constant pressure accumulators of an airplane, a rst relay operable in response to the operation of any one of said pump simulating means to control said pressure simulating means, a source of current, means vcontrolled by said pressure simulating means for deriving a potential from said source and for applying it to all of said indicators whereby said indicators show readings representative of the pressure in the accumulators prior to the operation of the unloading Valve of an airplane, a second relay operable in response to the operation of any oneof said pump simulating means, means controlled by said pressure simulating means for causing the release of said rst relay to arrest the operation of said pressure simulating means when said indicators show pressures of a predetermined value, and to derive and apply a reduced potential to said first indicator under the control of said second relay whereby said first indicator shows a reading representative of the hydraulic pressure in the opencenter portion of the hydraulic system of an airplane and said other indicators show hydraulic pressures in the constant pressure portion of the hydraulic system of an airplane following the operation of the unloading Valve.

19. In a ground trainer for aircraft ight personnel, means for simulating the production of hydraulic pressure, indicators for simulating the indication of the hydraulic pressure in the constant pressure accumulators of an airplane, means for simulating the operation of the foot vbrakes of an airplane, means controlled by the simulating means for deriving a decreasing pon tential from said source of current and for applying it to said indicators whereby said indicators are caused to show intermittently decreased readings representative of the decrease in pressure in the accumulators of an airplane incident to the repeated operation and release of the brakes.

20. In a ground trainer for aircraft night personnel, means for simulating the production of hydraulic pressure, indicators for simulating the indication of the hydraulic pressure in the constant pressure accumulators of an airplane, means for simulating the operation of the foot brakes of an airplane, means controlled by the repeated operation and release of said latter means for causing the intermittent operation of said pressure simulating means in a manner representative of the reduction of pressure in the constant pressure accumulators of an airplane incident to the operation of the brakes, a source of current, means controlled by said pressure simulating means for deriving a decreasing potential from said source and for applying it to said indicators whereby said indicators are caused to show intermittently decreasing readings representative of the decrease in pressure in the accumulators of an airplane incident to the repeated operation and release of the brakes, and means controlled by said pressure simulating means when the simulated pressure has been reduced to a predetermined value for arresting the operation of said pressure simulating means and for causing said indicators to show zero pressure readings representative of the reduction of pressure in the accumulators to zero.

ROBERT O. RIPPERE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,655,244 Rowell Jan. 3, 1928 2,099,857 Link Nov. 23, 1937 2,164,412 Koster July 4, 1939 2,218,546 Muller Oct. 22, 1940 2,327,997 Carmody Aug. 31, 1943 2,343,945 Weathers Mar. 14, 1944 l 2,346,838 Haight Apr. 18, 1944 2,366,603 Dehmel Jan. 2, 1945 2,372,741 Roberts Apr. 3, 1945 2,395,477 Gumley Feb. 26, 1946 2,406,221 Hornfeck Aug. 20, 1946 2,428,767 Albert Oct, 14, 1947 

